Cryogenic freezing and/or cooling of material, including food products, pharmaceuticals and the like, has become a commercial reality over the past decade and is in widespread use throughout the industrialized world. One piece of apparatus often employed in such cryogenic cooling is an elongated enclosure or tunnel through which the material is passed on an endless conveyor belt. The cryogen, such as liquid nitrogen, is injected into the tunnel and caused to undergo heat-exchange with the material carried on the conveyor resulting in the lowering of the temperature of the material to the desired level. Improvements in cooling and/or freezing systems of this general type have been constantly sought after.